Glasses,glass-ceramics and process for making same

ABSTRACT

Thermally crystallizable glasses of the R2O-RE2O3-Nb2O5-GF system wherein R is an alkali metal cation, RE is a rare earth metal cation, and GF is a glass former, namely, SiO2, GeO2 or P2O5, and transparent, translucent and opaque glass-ceramics made therefrom which have excellent dielectric properties, have high indices of refraction when the glass-ceramic is transparent and are suitable for use as capacitors and dielectrics, and for use in acoustooptical and electrooptical devices and the like. Also thermally crystallizable glasses of the R1O-RE2O3-Nb2O5-GeO2 system wherein R1 is a divalent metal cation and RE is a rare earth metal cation and such glasses have high indices of refraction usually above 2.00, and very low acoustic attenuation. These properties make the glasses and also the transparent glassceramics made therefrom ideally suited for use in acoustooptical and electrooptical devices wherein such properties are important to the efficient operation of such devices. Transparent and opaque glass-ceramics made from such glasses also have good dielectric properties including high dielectric constants and low dissipation factors. Glass-ceramics of the invention preferably have crystalline phases exhibiting the cubic perovskite structure or the tetragonal tungsten-bronze structure.

Umted Stat 36 f/ Rapp GLASSES, GLASS-CERAMICS AND PROCESS FOR MAKING SAME [75] Inventor: James Erich Rapp, Oregon, Ohio [73] Assignee: Owens-Illinois, Inc., Toledo, Ohio [22] Filed: June 9, 1972 [2]] App]. No.: 261,188

[56] References Cited UNITED STATES PATENTS l0/l971 Herczog et a1 106/52 7/1965 Herczog et al l06/39.6

3,029,152 4/1962 Milne 106/52 X 3,460,954 3/1969 Young 106/52 X 3,423,686 1/1969 Ballman 6! a1... 252/629 X 3,035,896 5/1962 Brixner I. l06/73.2 X 2,992,929 7/1961 Clement et a1. l06/73.2 X

3,422,018 l/I969 B61106 106/39.5 3,116,262 12/1963 Goodman l06/39.5 3,674,455 4/1972 Dugger 106/47 Q 3,573,939 4/1971 Beall 106/52 FOREIGN PATENTS 0R APPLICATIONS 977,835 3/1963 Great Britain 106/39.5

OTHER PUBLICATIONS lmoaka, M. et a1. Report of the Institute Industrial Sci- [451 Jan. 15, 1974 ence, March 1969 (pp. 161-193) 19(3) Three Component System Glass Formation Range II-a-Group Elements Germanate System".

Primary Examinerl-lelen M. McCarthy Att0rneyE. .I. Holler et al.

[ 5 7 ABSTRACT Thermally crystallizable glasses of the R O-RE O Nb O -GF system wherein R is an alkali metal cation, RE is a rare earth metal cation, and OP is a glass former, namely, SiO GeO or P 0 and transparent, translucent and opaque glass-ceramics made therefrom which have excellent dielectric properties, have high indices of refraction when the glass-ceramic is transparent and are suitable for use as capacitors and dielectrics, and for use in acoustooptical and electroopti c al devices and the like. Also thermally cry s tallizable glasses of the RO-RE O3-Nb O -GeO system wherein R is a divalent metal cation and RE is a rare earth metal cation and such glasses have high indices of refraction usually above 2.00, and very low acoustic attenuation. These properties make the glasses and also the transparent glass-ceramics made therefrom ideally suited for use in acoustooptical and electrooptical devices wherein such properties are important to the efficient operation of such devices. Transparent and opaque glass-ceramics made from such glasses also have good dielectric properties including high dielectric constants and low dissipation factors. Glassceramics of the invention preferably have crystalline phases exhibiting the cubic perovskite structure or the tetragonal tungsten-bronze structure.

38 Claims, No Drawings I 378 834 OR: IN 106/39u6 GLASSES, GLASS-CERAMICS AND PROCESS FOR MAKING SAME The advent of acoustooptical devices, electrooptical devices, and other devices utilizing transparent glasses and glass-ceramics has created a need for glasses and glass-ceramics having high indices of refraction and good light transmission properties. It is well-known, however, that the higher the index of refraction of a glass, the more difficult it is to obtain it in optical quality, i.e., free from bubbles, cords, stones, etc. This is especially true when the index of refraction is about 1.80 or higher.

While single crystal materials are of high quality and can be used in acoustooptical and electrooptical devices, they are relatively expensive to obtain, especially in large sizes and, moreover, one is limited to the precise index of refraction or dielectric constant and dissipation factor inherent in any particular single crystal.

The present invention is directed to certain compositions coming within the R O-RE O -Nb O -GF and R'O-RE O -Nb O -GeO system wherein R is an alkali metal cation selected from Na, K, Li, Rb, Cs; R is a divalent metal cation selected from Pb, Ba and Sr; RE is a trivalent metal cation of the rare earths of the group La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and includes other trivalent cations, such as Sc, Y In, Bi and the like. Wherever the term rare earth is used henceforth in this specification and claims, it is intended to include the trivalent cations listed above.

In the first system mentioned in the previous paragraph, in some instances R can be replaced in part by R 0 and in such event it must be kept in mind that the substitution is made in such a manner that one such divalent ion is used in lieu of two monovalent R ions to maintain the charge balance. The Glass Former is either GeO SiO or P 0 but should not be a mixture of two or more of these since a mixture of these glass formers tends to separate into two glass phases during the melting. In a specially preferred embodiment of the invention, the comp o sitions of the systems named have thfi formulas and R RENb5O 5 -xGeO2 where x is a number from 1 to 3 in an amount varying according to the particular R or R ion and the rare earth ion used. In such preferred compositions there is obtained a solid solution of alkali metal niobate or divalent metal niobate with the rare earth niobate to provide the desired cubic perovskite or tetragonal tungsten-bronze crystal structure in the glass'ceramic resulting from the heat treatment of the glass. The Glass Former should be present only in an amount sufficient to produce the glass of the desired composition having high dielectric constants and high indices of refraction which, when crystallized, will produce the necessary crystal structure sufficient to give the desired index of refraction and/or dielectric properties, and/or acoustooptical or electrooptical properties which properties are often improved in the glass-ceramics. Preferred crystal structures are the cubic perovskite and the tetragonal tungsten-bronze structures.

Glass ceramics of the present invention can be formed from the crystallizable glasses even though the glasses do not have any of the customary nucleating agents, such as TiO ZrO or the like. Glasses and transparent glass ceramics of this invention are suitable for use in electrooptical devices, acoustooptical devices and the like, including, for example, modulators, wave guides, laser Q-switches and/or deflectors, and the like. Certain of the glasses and glass ceramics have been found to also have good dielectric properties including high dielectric constants and low dissipation factors which make them suitable for use in a variety of electrical devices, such as capacitors, electroluminescent cells, and the like. Dielectric constants of at least about 50 (at room temperature and 0.5 MHz) with loss tangents or dissipation factors of less than 3 percent and preferably less than 1 percent are obtained with glass-ceramics of the present invention. The glassceramics of this invention can also be prepared in the form of small chips, of a size of about /4 inch and less, which are suitable as chip capacitors or can be ground into powder useful for screen printing of capacitors in electronic microcircuits.

The presence of the rare earth elements in the glasses and glass-ceramics imparts to these products the ability to fluoresce, i.e., when subjected to a source of appropriate radiation, they absorb this energy and emit light during irradiation and for a time thereafter, which time is usually measured in micro-seconds. This fluorescent property makes these glasses and glassweramics a valuable tool in the field of computer panels on which data is projected and viewed.

Furthermore, the formation of cubic perovskite crystals in certain of the transparent glass ceramics makes them potentially useful as laser materials. The presence of rare earth ions in the ordered structure of the crystal provides sharper absorption and emission bands for the fiuorescing phenomena, making the glass-ceramics ideally suited as lasers.

Included within the broad spectrum of the alkali metal oxide-rare earth oxide-Nb O Glass Former system of the invention, are the following compositions of the invention consisting essentially of the following oxides in the indicated mole percent ranges:

Ingredient Mole Percent SiO, 20-45 Nb,O, 34-50 Rare Earth Oxide 7-l0 z a) R,O 14-20 Ingredient Mole Percent SiO, 32-40 Nb,0 37-43 REG; 7 .5-'8 .5 R,0

wherein RE O and R are the same as identified above.

The compositions set forth in the following tables were prepared by melting together the glass former,

such as SiO GeO or P 0 the Nb O the rare earth 5 oxide and the alkali metal oxide or the divalent metal oxide in the mole percents given in the respective tables. In some instances the alkali metal oxides and the divalent metal oxides were charged as the respective carbonates.

In preparing the compositions, the raw materials or ingredients were batched and each of the batches was heated to a temperature sufficient to melt the ingredients and then held at that temperature for about 1-24 hours, the time being dependent on the specific composition and how long it took for the melting to be completed and a homogeneous melt to be formed. The melt was periodically stirred during this time. Each molten composition was then poured onto a metal plate and another metal plate placed over it to quench the composition. The glass-forming tendency of each composition was judged on the ability of the melt to be quenched into glass between the metal plates. Some of the'melts, and particularly the R'O-containing melts, to be discussed infra, were found to be stable enough to be poured into molds, rather than having to be quenched.

While those in the art can readily prepare the glasses disclosed in Table I, the batch materials and the respective amounts used are given below for representative glasses of Table 1.

Batch Materials Compositions (parts by weight) 7 8 Ottawa Silica 23 Quartz 27.8 27.9 27.4 29.4 28 Soda Ash 27.3 Potassium Carbonate 25.8 25.8 25.3 27.2 Cesium Carbonate 51.4 Niobium ()xide(Nh 169.9 123.6 124 121.6 130.3 103.2 Lanthanum Oxidc(La,O 42.1 25.9 Neodymium Oxidc(Nd,O,) 32 Praesodymium 0xidc(Pr,O 30.8 Dysprosium Oxide(Dy O,) 34.4 Yttrium Oxide(Y,O 22.4

Table I Compositions in Mole Percent Ingredient 1 2 3 4 5 6 7 8 9 10 SiO, 27.2 27.2 33.3 33.3 38.4 3 .4 38 4 4 38.4 9 w o, 45.5 45.5 41.7 41.7 38.5 38 5 38 5 38 5 38 5 7 Na,0 18.2

Cs,0 K 0 18.2 167 154 154 I54 I54 I54 I43 Rb,0 16.7 La,0, 9.1 9.1 8.3 8.3 7.7 7.14 Nd,0, 7.7

Gd O Dy,O 7.7 Sm,O:

Ingredient ll 12 I3 l4 l5 16 17 l8 19 2O 7 SiO, 42.9 42.9 42.9 42.9 2.9 20 33.3 42.9 38.4 33.3 Nb,0 35.7 35.7 35.7 35.7 35.7 41.7 35.7 38.5 41.7 N3 0 20 16.7 15.4 8.3

C820 14.3 K 0 14 3 14.3 8.4 Rb O 14.3 14 3 14.3 1.3,0 10 8.3 7.1 7.7 4.2

Nd O 7 l 7.l 4.1

Ingredient l 1 2 TABLE l-Continued 1300( /4) Yellow Pink Dielectric 272 142 118.4 Constant (R.T.,0.5

MHz)

Dissipation Factor (R.T-. 0.5 0.4 0.5 5.5 MHz) Opaque Glass Ceramic Heat Treatment Temp.F(Time,hrs)

Color Yellow Dielectric 262 l Constant (R.T., 0.5

MHz)

Dissipation Factor 0.6 0.8 (R.T., 0.5

MHz)

Crystal Phases Pink Transparent Opaque 4 1435(1 4) Colorless Yellow 185066) Colorless Grey 1600(lfi) Colorless Blue Blue

1550(5) Green Green 1350( V4) Yellow White *When Composition 2 was heated at I625F for two hours, a transparent glass-ceramic was formed containing a tetragonal tungsten bronze crystal structure.

Ingredient 9 10W 10 x 2.5 3 3 nD (Glass) 1.914

Dielectric Constant (R.T., 0.5 MHz) Temp.F(Time hrs) Color colorless Transparent Glass Ceramic Dielectric Constant (R.T.,0.5

MHz)

pink

blue

colorless V yellow-green pink Ingredient TABLE 1C0ntinued Dissipation Factor (R.T., 0.5 MHz) Opaque Glass Ceramic Heat Treatment Temp.F(Time,hrs)

purple Color Dielectric 4" Constant (R.T., 0.5 MHz) Dissipation Factor (R.T., 0.5 MHZ) C ry stal Phases n 1 Transparent Opaque Nut again green white purple white I nD(Glass) Dielectric Constant (R.T., 0.5 MHz) Dissipation Factor (R.T., 0.5 MHz) Transparent Glass Ceramic Heat Treatment Temp.F(Time,hrs) Color Transparent Glass Ceramic yellow 1350(16) 1400 /1 yellow 1250(3) yellow Transparent Opaque 190004 colorless yellow Mine The glasses of the invention wherein 810215 the glassformer have an index of refraction of at least 1.80 but preferably at least 1.90 and most preferably 2.00 and above. From Table 1, it can be seen that the index of refraction of the resulting glasses was quite high, namely about 1.900 and even above 2.000 for many of the glasses. When subjected to a heat treatment which crystallized certain of the glasses to a transparent glassceramic, the index of refraction of these ceramics was higher than that of the original glass in almost every in- 0.5 MHz) of less than 1 percent and preferably of less than 0.5 percent. The glass-ceramics have improved dielectric properties with the transparent glassceramics having a dielectric constant in excess of 50 and preferably in excess of I and even in excess of 150 up to about 300 or more with a dissipation factor of less than 2 percent and preferably less than about 1 percent. For the opaque glass ceramics, the dielectric constant is in excess of 75 and preferably in excess of 150 and up to 300 or more with dissipation factors of less than 2 percent and preferably less than 1 percent.

As is apparent from Table I, the dielectric constant of the resulting glasses and transparent and opaque glass-ceramics ranges from a low of about 50, actually 34.6 for the glass of Example 11, to over 100 and in some instances to over 200, as in Examples 1, 19 and 20. What is more important, however, and what makes the glass-ceramics particularly valuable in the electronics industry, is their extremely low dissipation factors. In a majority of the Examples, such dissipation factor is below 1 percent, making the glass-ceramics ideally suited for use as chip capacitors and dielectrics. Such glass-ceramics can also be ground to a powder and used to screen print capacitors for microelectronic circuits.

It has also been noted that the dielectric properties of the resulting glass-ceramics can be made to change, depending upon the heat treatment to which the respective glasses are subjected. This characteristic affords those in the art to make dielectrics with specific properties, rather than rely on the inherent property of a RzRENbion-1 crystal, per se.

The heat treatment for individual thermally crystallizable glasses of the invention will vary as to the temperature and the times at which they are held at each temperature. The temperature, of course, must be high enough to initiate and maintain the crystallization process in a controlled manner to obtain the desired glassceramic, whether it be transparent or opaque, within a reasonable time. It is known, for example, that certain glasses can be thermally in situ crystallized by keeping the glass heated at a low temperature, but at least above the annealing temperature, fora period of time, of days or weeks, until crystallization is complete. It is also known in the art that by subjecting a thermally crystallizable glass to higher temperatures, nucleation and eventually crystallization will occur in a much shorter period of time, sometimes in a matter of a few hours or even a few minutes.

The temperatures and times set forth in Table I are merely representative of those which may be successfully utilized in making the glass-ceramics of the invention. As shown with the compositions of Examples 1, 10, 16, 17, 19 and 20, different properties are-obtained in the glass-ceramics from the different heating schedules to which the precursor glasses are subjected. It is within the skill of those in the art, by routine testing, to subject the glasses to different temperatures and times and measuring the various properties obtained. In this manner one can ascertain particular values for dielectric constants, dissipation factors, indices of refraction,

etc.

The glass ceramics of the invention were examined by known X-ray diffraction techniques. The d-spacings of each crystal structure were calculated from the data published by B. A. Scott et al in an article appearing in Material Research Bulletin, Vol. 3, pages 831-842, 1968, and were compared with the X-ray results. The similarity of the observed d-spacings from the X-ray data and the calculated d-spacings from the above published data was used as a positive identification of the crystal phase.

The crystal phase or phases present in the glassceramics of the invention are identified by numbers in Table l and the numbers correspond to the following structures:

Nos.:

1 Cubic perovskite structure 2 Tetragonal tungsten-bronze structure 3 Unidentified phase in a tetragonal structure 4 A structure similarto pseudbctibic NaNbO 5 Unidentified The same numbers have the same meaning in Tables II and III.

The often preferred cubic perovskite structure was identified in the glass-ceramics of Compositions l, l6, l7 and 19 and the also preferred tetragonal tungstenbronze structure was identified in the glass-ceramics of Compositions 2, 6, l 1 and 20. When Composition 1 of Table I was heat treated at a temperature of l ,000F for 2 hours and l,300F for V4 hour, the crystal phase was ascertained to be the cubic perovskite structure. However, other glass-ceramics, where these two particular crystal structures were not observed, still had excellent indices of refraction and/or excellent dielectric properties.

The glasses and glass-ceramics of the invention have certain colors imparted thereto and, in some instances, the colors for the glass-ceramics are different from those of the glasses from which the glass-ceramics were made. Thus, the glasses and glass-ceramics are also useful as stones for costume jewelry, furniture inlays, and the like.

A number of compositions of the invention were also preparedin substantially the same manner as those in Table I except that 660: was used in lieu of SiOz as the glass former. The ingredients used to prepare the glasses were either the metal oxides set forth in Table II in the molar proportions disclosed therein, or batch materials similar to those used in making the compositions of Table 1, except that germania was used in lieu of the silica or quartz. Again, the alkali metal oxides were charged as alkali metal carbonates into the batches.

The glasses and glass-ceramics of the invention commg 'mfif fl'lf? TZJGQiEYOJNWh-Gb system, consist essentially of the following ingredients in the indicated ranges:

Ingredient Mole Percent GeO, 20-50 Nb,0, 30-50 RE O; 6-10 R,O 12-21 Ingredient Mole Percent GeO 20-45 M 0, 34-50 RE O 7-10 R 14-20 In a preferred embodiment of the compositions just defined, the compositions have the formula RZYENMO xGeO2 wherein x is a number from 1 to 4, usually 1 to 3, and glass-ceramics formed therefrom to contain crystals having a cubic perovskite or a tetragonal tungsten-bronze crystal structure.

In the most preferred embodiment of compositions of the R2O-RE2O 5-N b 2O5-GeO2 system, the compositions consist essentially of the following ingredients in the indicated mole percent.

wherein tlie RB O and the R are the same as defined above and the R20 includes Li20, Na2O,

K20, and CSzO.

Glasses and transparent glass-ceramics of the invention defined above and illustrated by representative examples in Table II have an index of refraction of at least about 1.95 and preferably over 2 and even over 2.1. Dielectric constants of the transparent glass-ceramics are at least and preferably over and can be as high as 50 and up to or more while the dielectric constants for the opaque glass-ceramics are at least 50 but more preferably over 150 and can go as high as 300 or more. The dissipation factors are as low as 2 percent and preferably as low as 1 percent and less. The opaque glass ceramics in particular have excellent dielectric properties including very low dissipation factors, as seen from Table II. Because of the high indices of refraction of the glasses, they are excellent for use in devices whrein such optical properties are required.

Furthermore, for some une lgpeetedreasons not fully understood, glasses formed with G602 as the glass former were much more stable than the glasses of Table I, which had SiO as the glass former. One would expect that the SiO containing glasses would be more stable, but such was not the case with the compositions ofTable II.

As also shown in Table II, glass-ceramics having a cubic perovskite crystal structure or a tetragonal tungsten bronze crystal structure can be obtained, as in Composition in Mole Percent Ingredient 2l 22 23 Y 24 GeO, Nb,O Na o K,O Rb,0 Li,O La O 9.1 8.3 7.1

Nd O B90,

nD (Glass) 2.ll5 2. Transparent Glass- Ceramic Heat Treatment Temp.F(Time, hours) 1200(V4) ll50(V4) Crystal Phases Yellow White Transparent l p Opaque 13000/4) ll50(l) castles.

Blue Yellow Grey White White Grey when composition 2| was heated at I475F for two hours, an opaque glass-ceramic was formed containing a crystalliilgphase exhibiting the cubic perovskite structure.

Compositions 21 and 25 respectively.

More importantly, it has been discovered that glasses Ingredient Mole Percent coming within the present embodiment of the invention are extremely useful in acoustoptical devices since, in Nb,0, 38-50 addition to the very high indices of refraction, they also R5303 have very low acoustic attenuation properties, lower 1540 than other known high index glasses. These acoustical H properties are set forth in Table V, infra, with respect Wherelll z a 1S rar art metal oxide as defined to Compositions 26 and 28 of Table II, and also with previously and R20 is an alkali metal Oxide, and p respect to Compositions 63 and 64 infra, which come 10 ferably is NazO, K20, Rb2O and Cs O or mixtures within the scope of the present embodiment of the inthereof. ventiom In a-preferred embodiment of the compositions just A number of compositions of the invention were pre- 1fi9 I c mpositions have the formul pared substantiallyin the same manner as those of Ta- 2 5 l5' 2 5 whe i X i a number of from 1 h1 1 d 1] except h P 0 was d as h' l to 2.5, and glass-ceramics formed therefrom have a former i of 0 or G The ingredients used cubic perovskite or a tetragonal tungsten bronze crystal to prepare the glasses were either the metal oxides Structure" set f th i T m I] i h molar proportions However, the most preferred compositions consist dosed therein, or in the case of tha alkali metal, essentially of the following ingredients in the indicated oxides, they were charged in the batch as alkalim lqfff ranges: meta] carbonates lngredient Mole Percent While those in the art can readily prepare the glasses P,o, 27-34 disclosed in Table Ill, the batch materials and the rew o, spective amounts used are given below for representa- R510:

. v R0 l6l8.5 tive glasses ofTable III. 7

Batch Materials Compositions (parts by weight) Potassium Phosphate 50.4 45.8 44.7 Sodium Phosphate 50.1 Ammonium Phosphate 20.7 36.7 34.3 Niobium Oxide Nb,o, 120.3 124.6 109.4 109.4 Potassium Carbonate 0.9 Neodynium Oxide Nap 3l.5 Lanthanum Oxide 1.3 0,) 30 Samarium Oxide (Sm O 28.6

Europium Oxide (Eu,0,)

cuts in the indicated mole percents:

Compositions of the invention wherein P O is the wherein REzOg and R20 are the same as defined glass-former consist essentially of the following ingredi- 40 above.

7 TKBLEW Compositions in Mole Percent Ingredient 31 32 llllll IIFOIIII U3 iFsl /TF Temp. F(Time,H rs) Color amber Transparent Glass Ceramic yellow pink grey col orless lll nlll Li qua w a -u -i qua pink blue colorless colorless TABLE 111 Crystal Phases white Transparent 5 Opaque When a glass body of composition 31 was heated at 1,750F for 2 hours, the transparent glass-ceramic that was formed had a tetragonal tungsten bronze crystal structure. Heating a glass body of composition 35 at l,- 500F for 2 hours and then at 1,525F for V4 hour resulted in an opaque glass-ceramic having a crystalline phase exhibiting the cubic perovskite structure. Likewise, when a glass body of composition 38 was heated 'at 1,350F for 2 hours and then at 1,500F for A hour,

the transparent glass-ceramic which was formed had an unidentified crystal phase of tetragonal structure. A glass body of the same composition 38, however, heat treated at 1,600F for 2 hours had a crystalline phase exhibiting the tetragonal tungsten-bronze structure.

Glasses of the invention having P 0 as the glass former have an index of refraction of at least 1.85 and preferably of at least 1.90 and above whereas the transparent glass-ceramics made therefrom have even higher indices of refraction, namely, at least 1.90 and preferably at least 2.00.

The index of refraction of the gasses containing P 05 is above 1.800. Upon heat treating the glasses to form transparent glass-ceramics, the index of refraction is increased, the amount of the increase depending upon the heat treatment to which the glass is subjected.

Furthermore, transparent glass-ceramics of the invention have dielectric constants of at least 40 and preferably of at least and even over 100 or more with a low dissipation factor of below 1 percent and preferably as low as 0.5 percent or lower. The opaque glass-ceramics of the present invention have a dielectric constant of at least and preferably over and up to or more with a dissipation factor of less than 2 percent and preferably less than 1 percent and, more preferably, less than 0.5 percent. Glass-ceramics of the invention make excellent capacitors and dielectrics.

Compositions in Mole Percent white pink blue white white Some of the glass-ceramics which were examined and tested for crystal structure had the cubic perovskite or the tetragonal tungsten-bronze structure as the crystal phase.

\Nhile the for egoing discussion of the invention for the most part relates to the RzO-RE O -NbzO g Glas s Former compositions, it has also been found that glasses and glass-ceramics of the R O-RE2O3-Nb2O5- GeO2 system wherein R is a divalent metal cation selected from Sr, Ba and Pb, and mixtures thereof have unexpectedly-high indices of refraction for the glasses, together with very good acoustical properties.

While in electrooptical devices the glass or glassceramic must be suitably transparent to light and usually has a high index of refraction, because of'the presence of highly polarizable ions, in accoustooptical devices the glass or transparent glass-ceramic must also have a low acoustic attenuation in addition to having a high index of refraction. The glasses of this embodiment of the invention have the lowest acoustic attenuation of any high index glasses known to the applicant.

Glasses of this embodiment of the invention consist essentially of the following ingredients expressed in mole percents:

Mole Percent wherein RE2O3 is a rare earth metal oxide as defined previously, RO is a divalent metal oxide selected from PbO, BaO and SrO, and mixtures thereof, and wherein up to about one-half of the moles of RO can be replaced by an equal number of moles of R 0. R is an alkali metal oxide such as Na O, K 0, Li O, Rb O, Cs O and mixtures thereof.

In a preferred embodiment of the compositions just defined, the compositions have the formula R 'RENb- O x GeO wherein x is a number of from 1.8 to 3.7.

.tions.

A number of representative glass and glass-ceramic compositions were prepared and their identity, together with the heat treatment schedules and the respective properties observed with respect to each composition are set forth in Tables IV, V and VII Ag ai nkach of the compositions were prepared in the same manner as the compositions of Table wherein each of the ingredients were mixed together and melted, the ingredients being present in the batches either as the respective oxides in the mole percents set forth in Table IV, or, in the case of BaO, SrO and alkali metal oxides, they were charged into the batches as barium carbonate, strontium carbonate and alkali metal carbonates, respectively.

TABCE IV &

Ingredient Compositions in Mole Percent GeO, Nb,O BaO SrO PbO

nD (Glass) L-L. LL11;

,w! l 2:33 'uLlio 1 1 a: at: u Lilli ww a:

Ingredient GeO, Nb O BaO SrO PbO La o Li O K 0 nD (Glass) Nullql 1..

o LA

Ingredient GeO, N E 0 BaO SrO PbO L 2 U 0 14,0

X nD (Glass) Mole Percent Ingredient wher'e'm'riago and R"6a re the same as'at'ave 555115 to about one-half of the moles of R 0 can be replaced til by an equal number of moles of R 0. R 0 is also the same as defined above in the broader range of composi- TABLE V Compositions Properties 39 40 42 43 46 47 48 50 51 A|(db/cm) 20 MHZ 1.63 1.19 1.24 1.5 1.26 1.77 2.04 l 53 2.52 60 MHz 1 4.22 5.4 4.20

100 M Hz 7.68 A,(db/cm) 20 MHz 5.97 2.95 3.28 1.82 2.24 3 44 60 MHz 12.6 V (mm/p. 5.326 5.13 2 4.939 5.049 5.091 5.021 5.393 5.369 5.233 sec.) V,(mm/p. 2.858 2.805 2.830 2.765 2.972 2,936

sec.)

A, acoustical attenuation for the longitudinal sound wave, expressed in decibels per centimeter. A, acoustical attenuation for the shear wave, expressed in decibels per centimeter. V, F velocity through the glass for the longitudinal wave, expressed in millimeters per micro-second. V velocity through the glass for the shear wave, expressed in millimeters per micro-second. MHz megahertz Properties 53 56 51 s 59 60 61 62 A (db/cm) V 20 MP1: i4 1 98 1 ?.40 l 19 168 i 1. 77 242 19 g 60 MHz 100 M Hz A.(db/cm) MHz 1.68 1.85 1.99 2.17 1.82 3.60

60 MHz V,(mm/p. 5.147 4.964 5.061 5.044 5.294 5.021 5.236 5.280 sec.) V,(mm/p. 2.776 2.781 2.779 2.937 2.765 2.982 sec.)

Properties 63 64 26 28 A,(db/cm) 20 MHZ 1.66 1.41 2.39 1.89 60 MHz 4.53 4.90 4.35 8.70 100 MHz 9.48 6.96 9.95 A,(db/cm) 20 MHz 3.88

60 MHz vV (mm/;t 5.402 5.246 5.589 5.522

sec.) V,(mm/p. 3.08 sec.)

Glasses 63 and 64 of Table V had the following compositions:

In gredient Mole Percent Glasses GeO, 42.9 Nb,0,, 31.3 35.7 La,0 6.2 7.1 Li,0 12.5 7.1 K,O 7.2 nD(Glass) 2.019 2.015

than 200 and up to 300 and more while the dissipation factor is less than 1 percent and preferably less than 0.5 percent. The opaque glass-ceramics have a dielectric constant of over 100 and preferably over 150 and a dissipation factor of less than 3 percent, but preferably less than 1 percent and, more preferably, less than 0.5

percent. 7

Several of the glasses in Table IV were heat treated to form glass-ceramics and properties of these glassceramics were measured and are set forth in Table V1. Again it was noted that the index of refraction of the transparent glass ceramics was higher than that of the corresponding glass. This is shown in the glass-ceramic of composition 42. Likewise, the dielectric constants of the glass ceramics were in excess of 100 and with the composition 42 and glass-ceramic, in excess of. 200. Dissipation factors were low in almost every instance, making the glass-ceramics suitable dielectrics for many purposes.

TABLE V1 Transparent Glass Ceramic yellow Heat Treatment Temp., "F (Time, Hrs.)

Color 7 Transparent nD Glass Ceramic Dielectric Constant (R.T.,0.5 MHZ) Dissipation Factor (R.T.,0.5 MHz) Opaque Glass Ceramic Heat Treatment 1350(2) 1500(2) 1400(2) Temp., "F (Time, Hrs.) Color white yellow gray T Dielectric Constant 159.3 11 1 (R.T.,0.5 MHz) Dissipation Factor,%

(R.T.,0.5 MHZ) 2.39 0.3

1 175( 16) 1350(V4) colorless 1175(16) 1350(14) colorless 135004) colorless Heat Treatment Temp., F (Time, Hrs.) Dielectric Constant (R.T.,0.5 MHz) Dissipation Factor (R.T.,0.5 MHZ)- Color v white white white Glasses consisting essentially of the following mole percent composition:

Ingredient Mole Percent Geo, 3045 40 1 32-43 1 .2 ,-.8:. 22. P120 13-22 can be thermally crystallized to form transparent glass ceramics having the desirable properties of the invention. Transparent glass ceramics of the foregoing composition range can also be obtained if up to one-half of the PbO is replaced by an equal number of moles of BaO or SrO or both, or if up to two-thirds of the PbO is replaced by an equal number of moles of L1 0, Na O or K 0 or mixtures thereof. Examples of such transparent compositions are examples 42, 54, 55, 56, S7, 58 and 59.

While the glasses and glass-ceramics of the invention have been discussed in terms of the sole essential ingreclients, it will be evident to those skilled in the art that minor amounts, preferably not more than 10 percent and most preferably no more than 5 percent by weight of other metal oxides which are compatible with the glass and glass-ceramic compositions can be used. Care should be taken, however, to insure that such other metal oxides do not materially affect the basic characteristics of the glasses and glass-ceramics of the present invention, including the high dielectric constants, low dielectric losses or dissipation factors, high indices of refraction, and low acoustic attenuation.

What is claimed is: e

l. A thermally crystallizable glass having an index of yellow 1200(2) "1 300( 14 yellow white yellow yellow 1425(2) 1450(V4) yellow white refraction of at least 1.80 and being suitable for crystallization to a glass-ceramic having a higher index of re- Ingredient Mole Percent S10, 20-45 Nb O; 34-50 R5303 7-10 mo 14-20 wherein RE O is a trivalent metal oxide selected from the group consisting of oxides of La, Nd,'Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Sc, Y, In and Bi and R 0 is an alkali metal oxide.

2. The thermally crystallizable glass as defined in claim 1 wherein said R 0 is a member selected from the group consisting of Na O, K 0, Rb O, C5 0 and mixtures thereof.

3. A glass-ceramic body having a dielectric constant in excess of 50 (Room temperature, 0.5MI-lz) and a dissipation factor of less than 2 percent, said glass ceramic prepared by thermally in situ cyrstallizing a thermally crystallizable glass consisting essentially of the following ingredients in mole percent:

7 1n gredient wherein RE2O3 is a trivalent metal oxide selected from the group consisting of oxides of La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, ER, Tm, Yb, Sc, Y, In and Bi and R is an alkali metal oxide.

4. The glass-ceramic body as defined in claim 3 wherein said glass-ceramic is transparent and has an index of refraction of at least 1.90.

5. The glass, ceramic body as defined in claim 3 wherein said glass-ceramic is transparent and has an index of refraction of at least 2.00.

6. The glass-ceramic body as defined in claim 3 wherein said glass-ceramic body has a dielectric constant in excess of 150 (Room Temperature, 0.5MHz) and a dissipation factor of less than 1 percent.

7. A glass-ceramic body prepared by thermally in situ crystallizing a thermally crystallizable glass of thecomposition R RENb O -x SiO2 wherein R is an alkali metal cation, RE is a trivalent metal cation selected from the group consisting of La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Sc, Y, In and Bi and x is a number of from 1 to 3, said glass ceramic body having a crystal structure selected from the group consisting of cubic perovskite crystal structure and tetragonal tungstenbronze crystal structure.

8. The glass-ceramic body as defined in claim 3 wherein said thermally crystallizable glass consists essentially of the following ingredients in mole percent:

Ingredient Mole Percent "576% A 32-40 Nbzos 37-43 REzOa 7.5-8.5 R l5-l7 9. A thermally crystallizable glass having an index of refraction of at least about l.95 and low acoustic attenuation properties, said glass consisting essentially of the following ingredients in mole percent:

Ingredient Mole percent EET); W 10-50 Nbzos 30-50 REzoa 6-10 R 0 l2-Zl Ingredient Mole percent GeO: 20-45 NbZOS 34-50 REgOu 7-10 R20 14-20 10. A thermally crystallizable. glass having an index of refraction of at least about 1.95 and low acoustic attenuation properties, said glass consisting essentially of the following ingredients in mole percent:

Ingredient V Mole Percent GeO2 32-40 Nbzos 37-42 REzOs 7.5-8.5 R20 l5-l7 and wherein RE O is a trivalent metal oxide selected from the group consisting of oxides of La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Trn, Yb, Sc, Y, In and Bi and R20 is an alkali metal oxide.

11. The thermally crystallizable glass as defined in claim 9 wherein said index of refraction is in excess of 2.00.

12. A glass-ceramic body prepared by thermally in situ crystallizing a thermally crystallizable glass of the composition R RENb O15-x GeO2 wherein R is an alkali metal cation, RE is a trivalent metal cation selected from the group consisting of La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Sc, Y, in and Bi and x is a number of from 1 to 4, said glass-ceramic body containing crystals having a crystal structure selected from the group consisting of cubic perovskite crystal structure and tetragonal tungsten-bronze crystal structure.

13. A glass-ceramic body prepared by thermally in situ crystallizing a thermally crystallizable glass of the composition R RENb OiS-x G602 wherein R is an alkali metal cation, RE is a trivalent metal cation selected from the group consisting of La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Sc, Y, In and Bi and x is a number of from 1 to 3, said glass-ceramic body containing crystals having a crystal structure selected from the group consisting of cubic perovskite crystal structure and tetragonal tungsten-bronze crystal structure.

14. A glass-ceramic body prepared by thermally crystallizing a thermally crystallizable glass consisting essentially of the following ingredients in mole percent:

Ingredient Mole Percent wherein RE2O is a trivalent metal oxide selected from the group consisting of oxides of La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Sc, Y, In and Bi and R20 is an alkali metal oxide.

15. A glass-ceramic body having a dielectric constant in excess of at least 35 (Room Temperature, 0.5 MHz) and a dissipation factor of less than 2 percent, said glass-ceramic prepared by thermally in situ crystallizing a thermally crystallizable glass defined in claim 9.

16. The glass-ceramic body as defined in claim 15 wherein said glass-ceramic is transparent and has an index of refraction of over 2.00 and a dielectric constant in excess of 50 and a dissipation factor of less than 2 percent.

17. A thermally crystallizable glass having an index of refraction above 1.80 and being suitable for in situ cry stalliiation to a glass-ceramic havmg a higher index of refraction, a dielectric constant 25 (R.T., 0.5 MHZ) of at least 40 and a dissipation factor of lestlfin 2 percent, said glassYonsistin g essentially of the following ingredients in mole percent:

- 24. The glass-ceramic body as defined in claim 20 wherein said body has a dielectric constant of at least 1 percent. 5 25. A glass-ceramic body prepared by thermally in situ crystallizing a thermally crystallizable glass of the Ingredient Mole Percent composition R RENb O .x P wherein R is an alkali P o 2040 metal cation, RE is a trivalent metal cation selected 1 2 3840 from the group consisting of La, Nd, Sm, Eu, Gd, Tb, R520, 7-10 10 Dy, Ho, Er, Tm, Yb, Sc, Y, In and Bi and x is a number 5-20 of from 1 to 2.5, said glass ceramic body having a crystal structure selected from the group consisting of cubic perovskite crystal structure and tetragonal tungwherein RE O is a trivalent metal oxide selected from sten-bronze crystal structure. the group consisting of oxide of La, Nd, Sm, Eu, Gd, 26. A thermally crystallizable glass having an index Tb, Dy, Ho, Er, Tm, Yb, Sc, Y, In and Bi and R 0 is of refraction of at least 2.00 and low acoustical attenuan alkali metal oxide or mixtures of alkali metal oxides. ation properties, said glass consisting essentially of the following ingredients in mole percent:

18. The thermally crystallizable glass as defined in claim 17 wherein said R 0 is a member selected from 20 the group consisting of Na O, K 0, Rb O, Cs O and Mme mixtures thereof. Geo: 3047 19. The thermally crystallizable glass as defined in 32-43 claim 17 wherein said glass consists essentially of the $8 &3; following-ingredients in mole percent: 5

wherein RE O is a trivalent metal oxide selected from lngred'em Mme the group consisting of oxides of La, Nd, Sm, Eu, Gd,

p205 Tb, Dy, Ho, Er, Tm, Yb, Sc, Y, In and Bi and RO is 2: 8: :3; a divalent metal oxide selected from the group consist- 18.5 ing of PbO, BaO and SrO and mixtures thereof.

27. The thermally crystallizable glass as defined in claim 26 wherein up to about one-half of said R 0 is re- 20. A glass-ceramic body having a dielectric constant placed by an equal mole percent of an alkali metal ox- (R.T., 0.5 MHz) of at least 40 and a dissipation factor 35 ide. of less than 2 percent, said glass-ceramic prepared by 28..A thermally crystallizable glass having an index thermally in situ crystallizing a thermally crystallizable of refraction of at least 2.00 and low acoustical attenuglass consisting essentially of the following ingredients ation properties, said glass consisting essentially of the in mole percent: 40 following ingredients in mole percent:

ingredient Mole Percent Ingredient Mole Percent :50, 20-40 Geo, 33-44 RE,0, 7-10 RED, 7-8.5

11,0 15-20 R'O l4-l7 wherein RE O is a trivalent metal oxide selected from wherein RE O: is a trivalent metal oxide selected from the group consisting of oxides of La, Nd, Sm, Eu, Gd, the group consisting of oxides of La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Sc, Y, In and Bi and R 0 is Tb, Dy, Ho, Er, Tm, Yb, Sc, Y, In and Bi and R'O is an alkali metal oxide or mixtures of alkali metal oxide. a member selected from the group consisting of PbO,

SrO and BaO and mixtures thereof.

21. The glass-ceramic body of claim 20 wherein said I 29. A transparent glass-ceramic body having a high thermally crystallizable glass consists essentially of the index of refraction and low acoustical attenuation following ingredients in mole percent: properties,'said glass ceramic formed by thermal in situ crystallization of a thermally crystallizable glass consisting essentially of the following ingredients in mole Ingredient Mole Percent percent:

213:), 21.22 RE,0, 8-9.5 Ingredient Mole Percent R,o 1648.5

Geo, 3047 w o, 32-43 22. The glass-ceramic body as defined in claim 20 6 &3;

wherein said glass-ceramic is transparent and has an index of refraction of at least 1.90.

23. The glass-ceramic body as defined in claim 20 wherein said glass-ceramic is transparent and has an index of refraction of at least 2.00.

wherein RE O is a trivalent metal oxide selected from the group consisting of oxides of La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Sc, Y, In and Bi and RO is a divalent metal oxide selected from the group consisting of PhD, BaO and SrO and mixtures thereof.

30. The transparent glass-ceramic body as defined in claim 29 wherein up to about one-half of said R'O is replaced by an equal mole percent of an alkali metal oxide.

31. A transparent glass-ceramic body having a high index of refraction and low acoustical attenuation properties, said glass-ceramic formed by thermal in situ crystallization of a thermally crystallizable glass consisting essentially of the following ingredients in mole percent:

Ingredient Mole Percent GeO, 33-44 Nb,0,, 35-42 RE O 7-8.5 RO 14-17 Ingredients Mole Percent GeO, 30-47 Nb205 32-43 L2 6.5-8.5 PbO 13-22 33. A glass-ceramic body prepared by thermally in situ crystallizing a thermally crystallizable glass of the composition RRENb O, .x GeO wherein R is a divalent metal cation selected from Sr, Ba and Pb and mixtures-thereof, RE is a trivalent metal cation selected from the group consisting of La, Nd, Sm, Eu, Gd, Tb, Dy, H0, Er, Tm, Yb, Sc, Y, In and Bi ane x is a number from 1.8 to 3.7, said glass-ceramic body having a crystal structure selected from the group consisting of cubic perovskite crystal structure and tetragonal tungsten-bronze crystal structure.

34. A glass-ceramic body formed by thermal in situ crystallization of a thermally crystallizable glass consisting essentially of the following ingredients in mole percent:

Ingredient Mole Percent Geo, 30-47 mp, 32-43 115,0, 6.5-8.5 R 0 l3-22 wherein REl O is a trivalent metal oxide selected from the group consisting of oxides of La, Nd, Sm, Eu, Gd, Tb, Dy, l-Io, Er, Tm, Yb, Sc, Y, In and Bi and R 0 is a divalent metal oxide selected from SrO, BaO and PhD and mixtures thereof, said body having a dielectric constant (R.T., 0.5 MHz) greater than and a dissipation factor of less than 3 percent.

35. The glass-ceramic body of claim 34 wherein said body has a dielectric constant R.T., 0.5 MHz) greater than 200 and a dissipation factor of less than 3 percent.

36. The glass-ceramic body of claim 34 wherein said dissipation factor is less than 1 percent.

37. Glasses thermally crystallizable to transparent glass-ceramics consisting essentially of the following ingredients:

Ingredients Mole Percent Geo 30-45 a s 3 2-43 L3 0; 6 .5-8 5 PbO 1 3-22 wherein up to one-half of the PbO can be replaced by an equal number of moles of BaO, or SrO or both, and wherein up to two-thirds of the PhD can be replaced by an equal number of moles of Li O, Na O or K 0 or mixtures thereof.

38. A transparent glass ceramic made by thermal crystallization of a glass of claim 37.

P0405) UNITED STATES PATENT OFFICE 56 CERTIFICATE OF CORRECTION Patent No. 3,785,83 Dated January 15, 197i Inventofl s) James Erich. Rapp It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2 line 5 0 x 810 shouldbe O 5 x 810 Column 13, Composition 31 line- Same-1:11am Oxide, delete -"28-6"; Column .13, Composition 32, line Samarium. Oxide, insert. 2856 Table V, Column 19, under Proper-ties,- second occurrence line 5, "A. (db/cm)" should be --A (db/cm)-. Claim 9, first line under Mole percent, "10-50" should be 20-50 Claim 27, second line, "R 0" should be --R O-- Signed andsealed this 29th day of October 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. 0. MARSHALL DANN Commissioner of Patents Attesting Officer 

2. The thermally crystallizable glass as defined in claim 1 wherein said R2O is a member selected from the group consisting of Na2O, K2O, Rb2O, Cs2O and mixtures thereof.
 3. A glass-ceramic body having a dielectric constant in excess of 50 (Room temperature, 0.5MHz) and a dissipation factor of less than 2 percent, said glass ceramic prepared by thermally in situ crystallizing a thermally crystallizable glass consisting essentially of the following ingredients in mole percent:
 4. The glass-ceramic body as defined in claim 3 wherein said glass-ceramic is transparent and has an index of refraction of at least 1.90.
 5. The glass ceramic body as defined in claim 3 wherein said glass-ceramic is transparent and has an index of refraction of at least 2.00.
 6. The glass-ceramic body as defined in claim 3 wherein said glass-ceramic body has a dielectric constant in excess of 150 (Room Temperature, 0.5MHz) and a dissipation factor of less than 1 percent.
 7. A glass-ceramic body prepared by thermally in situ crystallizing a thermally crystallizable glass of the composition R2RENb5O15.x SiO2 wherein R is an alkali metal cation, RE is a trivalent metal cation selected from the group consisting of La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Sc, Y, In and Bi and x is a number of from 1 to 3, said glass ceramic body having a crystal structure selected from the group consisting of cubic perovskite crystal structure and tetragonal tungsten-bronze crystal structure.
 8. The glass-ceramic body as defined in claim 3 wherein said thermally crystallizable glass consists essentially of the following ingredients in mole percent:
 9. A thermally crystallizable glass having an index of refraction of at least about 1.95 and low acoustic attenuation properties, said glass consisting essentially of the following ingredients in mole percent:
 10. A thermally crystallizable glass having an index of refraction of at least about 1.95 and low acoustic attenuation properties, said glass consisting essentially of the following ingredients in mole percent:
 11. The thermally crystallizable glass as defined in claim 9 wherein said index of refraction is in excess of 2.00
 12. A glass-ceramic body prepared by thermally in situ crystallizing a thermally crystallizable glass of the composition R2RENb5O15.x GeO2 wherein R is an alkali metal cation, RE is a trivalent metal cation selected from the group consisting of La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Sc, Y, In and Bi and x is a number of from 1 to 4, said glass-ceramic body containing crystals having a crystal structure selected from the group consisting of cubic perovskite crystal structure and tetragonal tungsten-bronze crystal structure.
 13. A glass-ceramic body prepared by thermally in situ crystallizing a thermally crystallizable glass of the composition R2RENb5O15.x GeO2 wherein R is an alkali metal cation, RE is a trivalent metal cation selected from the group consisting of La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Sc, Y, In and Bi and x is a number of from 1 to 3, said glass-ceramic body containing crystals having a crystal structure selected from the group consisting of cubic perovskite crystal structure and tetragonal tungsten-bronze crystal structure.
 14. A glass-ceramic body prepared by thermally crystallizing a thermally crystallizable glass consisting essentially of the following ingredients in mole percent:
 15. A glass-ceramic body having a dielectric constant in excess of at least 35 (Room Temperature, 0.5 MHz) and a dissipation factor of less than 2 percent, said glass-ceramic prepared by thermally in situ crystallizing a thermally crystallizable glass defined in claim
 9. 16. The glass-ceramic body as defined in claim 15 wherein said glass-ceramic is transparent and has an index of refraction of over 2.00 and a dielectric constant in excess of 50 and a dissipation factor of less than 2 percent.
 17. A thermally crystallizable glass having an index of refraction above 1.80 and being suitable for in situ crystallization to a glass-ceramic having a higher index of refraction, a dielectric constant (R.T., 0.5 MHz) of at least 40 and a dissipation factor of less than 2 percent, said glass consisting essentially of the following ingredients in mole percent:
 18. The thermally crystallizable glass as defined in claim 17 wherein said R2O is a member selected from the group consisting of Na2O, K2O, Rb2O, Cs2O and mixtures thereof.
 19. The thermally crystallizable glass as defined in claim 17 wherein said glass consists essentially of the following ingredients in mole percent:
 20. A glass-ceramic body having a dielectric constant (R.T., 0.5 MHz) of at least 40 and a dissipation factor of less than 2 percent, said glass-ceramic prepared by thermally in situ crystallizing a thermally crystallizable glass consisting essentially of the following ingredients in mole percent:
 21. The glass-ceramic body of claim 20 wherein said thermally crystallizable glass consists essentially of the following ingredients in mole percent:
 22. The glass-ceramic body as defined in claim 20 wherein said glass-ceramic is transparent and has an index of refraction of at least 1.90.
 23. The glass-ceramic body as defined in claim 20 wherein said glass-ceramic is transparent and has an index of refraction of at least 2.00.
 24. The glass-ceramic body as defined in claim 20 wherein said body has a dielectric constant of at least 65 (R.T., 0.5 MHz) and a dissipation factor of less than 1 percent.
 25. A glass-ceramic body prepared by thermally in situ crystallizing a thermally crystallizable glass of the composition R2RENb5O15.x P2O5 wherein R is an alkali metal cation, RE is a trivalent metal cation selected from the group consisting of La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Sc, Y, In and Bi and x is a number of from 1 to 2.5, said glass ceramic body having a crystal structure selected from the group consisting of cubic perovskite crystal structure and tetragonal tungsten-bronze crystal structure.
 26. A thermally crystallizable glass having an index of refraction of at least 2.00 and low acoustical attenuation properties, said glass consisting essentially of the following ingredients in mole percent:
 27. The thermally crystallizable glass as defined in claim 26 wherein up to about one-half of said R1O is replaced by an equal mole percent of an alkali metal oxide.
 28. A thermally crystallizable glass having an index of refraction of at least 2.00 and low acoustical attenuation properties, said glass consisting essentially of the following ingredients in mole percent:
 29. A transparent glass-ceramic body having a high index of refraction and low acoustical attenuation properties, said glass ceramic formed by thermal in situ crystallization of a thermally crystallizable glass consisting essentially of the following ingredients in mole percent:
 30. The transparent glass-ceramic body as defined in claim 29 wherein up to about one-half of said R1O is replaced by an equal mole percent of an alkali metal oxide.
 31. A transparent glass-ceramic body having a high index of refraction and low acoustical attenuation properties, said glass-ceramic formed by thermal in situ crystallization of a thermally crystallizable glass consisting essentially of the following ingredients in mole percent:
 32. A transparent gLass-ceramic body having a high index of refraction and low acoustical attenuation properties, said glass ceramic formed by thermal in situ crystallization of a thermally crystallizable glass consisting essentially of the following ingredients in mole percent:
 33. A glass-ceramic body prepared by thermally in situ crystallizing a thermally crystallizable glass of the composition R1RENb5O15.x GeO2 wherein R1 is a divalent metal cation selected from Sr 2, Ba 2 and Pb 2 and mixtures thereof, RE is a trivalent metal cation selected from the group consisting of La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Sc, Y, In and Bi and x is a number from 1.8 to 3.7, said glass-ceramic body having a crystal structure selected from the group consisting of cubic perovskite crystal structure and tetragonal tungsten-bronze crystal structure.
 34. A glass-ceramic body formed by thermal in situ crystallization of a thermally crystallizable glass consisting essentially of the following ingredients in mole percent:
 35. The glass-ceramic body of claim 34 wherein said body has a dielectric constant (R.T., 0.5 MHz) greater than 200 and a dissipation factor of less than 3 percent.
 36. The glass-ceramic body of claim 34 wherein said dissipation factor is less than 1 percent.
 37. Glasses thermally crystallizable to transparent glass-ceramics consisting essentially of the following ingredients:
 38. A transparent glass ceramic made by thermal crystallization of a glass of claim
 37. 